1. Field of the Invention
The present invention relates to a processing apparatus for providing a predetermined processing to a processing object such as a semiconductor wafer.
2. Description of the Related Art
There have been known various types of processing apparatus for providing a predetermined processing to a processing object. For example, in a semiconductor manufacturing process, there have been used various types of processing apparatus for providing processings such as forming an oxide film on a processing object such as a semiconductor wafer (hereinafter simply called as wafer), forming a thin film by a thermal CVD, or forming an impurity concentration region by a thermal diffusion method.
As such a processing apparatus, the processing apparatus of a horizontal type is conventionally used, and the processing apparatus of a vertical type has been often used in recent years. In the processing apparatus of the vertical type, in a state that a wafer boat containing a large number of wafers is inserted into substantially a cylindrical heated processing tube (hereinafter called as process tube) in a high temperature atmosphere, a predetermined process gas is introduced to the process tube, so that various types of processings can be provided to the wafer.
FIG. 4 shows one example of the processing apparatus of the vertical type. As shown in the figure, a manifold 2 is provided below a process tube 1 made of quartz. Gas can be supplied and exhausted to/from the process tube 1 by an exhaust pipe 3 and a gas supply tube 4 provided in the manifold 2. In the outside of the process tube 1, cylindrical heaters 5 are provided to enclose the process tube 1. By use of the heaters 5, the inside of the process tube 1 can be controlled to a desired temperature. The wafer boat 7 containing the large number of wafers W is inserted into the process tube 1 from a transfer chamber 10 by a boat elevator 11a constituting a transfer mechanism. Then, a flange 7a of the wafer boat 7 is brought in contact with a flange section 2a of the manifold 2 in a sealed state, so that the process tube 1 is closed.
In the load lock chamber 140 provided adjacent to the transfer chamber 140, there are provided wafer carrier C and wafer transfer means 150. The wafer carrier C is transferred by wafer transfer means 150. The transfer means 150 is used to transfer the wafer W contained in the wafer carrier C to the wafer boat 7, or transfer the wafer W mounted on the wafer boat 7 to the wafer carrier C.
For providing a predetermined processing to the wafer W by use of the above-structured processing apparatus, the wafer carrier C is transferred to the load lock chamber 140 through a front door 21 by carrier transfer means. Then, the wafer W contained in the wafer carrier C is stored in the wafer boat 7 through a rear door 22 by wafer transfer means 150 in a state that the inside of the load lock chamber 140 is isolated from outside air, for example, under an inactive gas atmosphere such as nitrogen (N.sub.2) (non-oxygen atmosphere). Thereafter, the wafer boat 7 is lifted by the elevator 11a and transferred to the process tube 1, and the process tube 1 is maintained to be in an air-tight state. Thereafter, gas of the process tube 1 is exhausted through the exhaust pipe 3, and the inside of the process tube 1 is set to be a predetermined vacuum state. If the inside of the process tube 1 reaches the predetermined vacuum state, process gas is introduced to the process tube 1 through the gas supply pipe 4, and a desired processing is provided to the wafer W. After processing, the process gas of the process tube 1 is exhausted through the exhaust pipe 3, and the inside of the process tube 1 is set to be a predetermined vacuum state. Thereafter, N.sub.2 gas is introduced to the process tube 1 through the gas supply pipe 4. Then, at the time when N.sub.2 gas pressure of the process tube 1 is the same as N.sub.2 gas pressure of the transfer chamber 10, the wafer boat 7 is moved down, and the wafer boat 7 is transferred from the process tube 1. Then, by wafer transfer means 150, the processed wafer W, which is set to the wafer boat 7, is contained in the wafer carrier C of the load lock chamber 140.
In the processing by use of the above processing apparatus of the vertical type, a portion close to an opening section of the process tube 1 is in a considerable high temperature atmospheric state when the wafer W is transferred with the wafer boat 7 from the transfer chamber 10 to the process tube 1 or the wafer W is transferred with the wafer boat 7 from the process tube 1 after processing. Due to this, if air exists there, there is a problem in that a natural oxide film is formed on a surface of the wafer W by oxygen (O.sub.2) of air.
Also, in this type of the processing apparatus for repeating the processing of the wafer W, gaseous impurities such as carbon are generated in the transfer chamber 10, or particle impurities such as oil mist or dust are easily generated. Therefore, if these impurities exist in the transfer chamber 10, impurities are adhered to the wafer W or a chemical reaction occurs, and a characteristic of the semiconductor element is deteriorated, or yield is lowered.
Moreover, the temperature in N.sub.2 gas atmosphere of the transfer chamber 10 is abnormally increased by bleedoff of hot air from the process tube 1 or radiant heat from the the processed wafer W heated at a high temperature.
In consideration of the above problems, in a state that the transfer chamber 10 is maintained in an air-tight state, the wafer boat 7 is transferred to/from the process tube 1 under an inactive gas atmosphere (non-oxygen atmosphere) such as N.sub.2 gas, and air of the transfer chamber 10 is always changed. Thereby, the inside of the transfer chamber 10 is maintained in a clean atmosphere that no atmospheric air enters. Also, the transfer chamber 10 is prevented from being filled with hot air. More specifically, in order to prevent air from entering from the outside, the atmosphere of the transfer chamber 10 is always maintained to be positive pressure. Also, clean inactive gas, serving as purge gas, is always introduced to the transfer chamber 10 through a gas supply pipe 12, while inactive gas of the transfer chamber 10 are always exhausted to the outside through an exhaust pipe 13 together with impurities, and the inactive gas atmosphere of the transfer chamber 10 is maintained to be positive pressure and high purity.
However, even if only the transfer chamber 10 is maintained to be positive and high purity, the above-mentioned problems cannot be fully solved if the circulation of outside air to the load lock chamber 140 which the wafer W is transferred to/from is left as it is. Due to this, the following method is used.
More specifically, at the time when the wafer carrier C stored in the wafer W is transferred to the load lock chamber 140, the front door 21 is closed, and the inside of the load lock chamber 140 is closed. Thereafter, air left in the load lock chamber 140 is exhausted, and atmosphere of the load lock chamber 140 is purged by inactive gas. According to this method, the wafer W is transferred to the chamber 10 from the load lock chamber 140 through the rear door 2 in a clean atmosphere where inactive gas is substituted for air.
By the way, normally, the wafer carrier C can store a plurality of wafers W such as 25 wafers W. Also, the wafer boat 7 can store 50 to 100 wafers W. Therefore, in a case that the wafer boat 7 can store 100 wafers W and the wafer carrier C can store 25 wafers W, it is needed that four wafer carriers C be set in a standby state in the load lock chamber 140 in transferring the wafers W to the wafer boat 7 of the transfer chamber 10 from the load lock chamber 140. Also, since wafer transfer means 150 is also provided in the load lock chamber 140, the load lock chamber 140 has inevitably a large capacity. Only if the transfer chamber 10 is maintained to be positive pressure and high purity as the supply and exhaust of inactive gas to/from the transfer chamber 10 are always performed, a large quantity of inactive gas is consumed. In addition to this, if atmosphere of the load lock chamber 140 having a large capacity is purged by inactive gas, the total amount of consumption of inactive gas becomes considerable. From an economical viewpoint, this processing costs much, and is unfavorable. In actual, the transfer chamber 10 and the load lock chamber 140, which have about 1 meter in depth and about 2 meters in height, are largely box-shaped. Due to this, for substitute inactive gas for air of the inside of each of these chambers at first, a large amount of inactive gas must be introduced thereto, it takes much time to perform a sufficient gas substitution, and efficiency of processing is lowered. To solve this problem, there can be considered a method in which the inside of each of the transfer chamber 10 and the load lock chamber 140 is vacuumed by a vacuum pump and inactive gas is newly introduced into these chambers. However, according to this method, it is required that a housing panel structure of the apparatus body including the transfer chamber 10 and the load lock chamber 140 be made of steel having high airtightness and thickness enough to withstand negative pressure. Due to this, increase in manufacturing cost may be brought about.
Moreover, the wafer carrier C is exposed in air before being transferred to the load lock chamber 140, and is put in a an easily contaminated state. Due to this, the inside of the load lock chamber 140 is purged in a state that the contaminated wafer carrier C is transferred to the load lock chamber 140. Therefore, the above method is not a favorable method in improving the purge effect.